DESCRIPTION: The first series of experiments seeks to provide data on the role of color in segmentation. The second series of experiments investigates whether illusory contours can add to real contours by adding a contrast edge in the region of an illusory contour and looks at the effect of the illusory contour on its detectability. The third series of experiments investigates how shadows influence judgements of shape and object recognition. The final series of experiments seeks to understand 'object invariance.'